1. Technical Field
The present disclosure refers to the field of electronic circuits using the current reuse technique.
2. Discussion of the Related Art
The necessity of obtaining higher gains while reducing absorbed power has led to the design of different kinds of multi-stage amplifiers based on the direct current reuse principle. These approaches, which are generally referred as “current reuse” techniques, substantially consist of two main types: capacitive coupling techniques and resonant series inter-stage LC networks.
The following reviews refer to the capacitive coupling technique:                C-Y. Cha, S-G. Lee, “A low power, high gain LNA topology,” in ICMT 2000, pages 49-52.        G. Gramegna, A. Magliarisi, M. Paparo, “An 8.2-GHz, 14.4 mW, 1.6 dB NF SiGe bipolar LNA with DC current reuse,” in BCTM 2003, pages 49-52.        J. S. Walling, S. Shekhar and D. J. Allstot, “A gm-boosted current-reuse LNA in 0.18 μm CMOS,” in RFIC 2007, pages 613-617.        
For example, the paper “A low power, high gain LNA topology” Y. Cha, S-G. Lee shows a first MOSFET transistor having its drain connected to the gate of a second MOSFET transistor by a coupling capacitor. The first transistor drain is also connected to the second transistor source by an inductor. The coupling for the radiofrequency signal between the first and second transistors is ensured by the coupling capacitor. Further, a decoupling capacitor is connected across the second transistor source and the ground and operates as a bypass for the radiofrequency signal and as an open circuit for the direct current, for ensuring in this way the current reuse between the two transistors. The path for the direct current is as the path of a cascode amplifier, while the path for the RF signal is as the one of a common source two stage amplifier having an inductive load.
It is to be observed that this technique is adapted for frequencies lower than a GHz, due to the presence of parasitic capacities in the first transistor drain, which result in a radiofrequency signal partition and in an inefficient transfer to the second transistor.
The following reviews refer to the current reuse technique with resonant series inter-stage LC networks:                C-Y. Cha, S-G. Lee, “A 5.2-GHz LNA in 0.35-μm CMOS utilizing inter-stage series resonance,” IEEE JSSC 2003, pages 669-672.        C-H. Liao, and H-R. Chuang, “A 5.7-GHz 0.18-μm CMOS gain-controlled differential LNA with current reuse for WLAN receiver,” IEEE MWCL 2003, pages 526-528.        
The paper “A 5.2-GHz LNA in 0.35-μm CMOS utilizing inter-stage series resonance”, C-Y. Cha, S-G. Lee describes a circuit analogous to the above mentioned one, wherein, however, the RF signal coupling between the two cascade stages is obtained by a LC network. In this case, the inductor and capacitor are sized to obtain a series resonance for the RF signal, in order to obtain a low impedance at the operative frequency and improve the signal transfer between the transistors. This technique enables absorption of the parasitic capacities and therefore is adapted to operate also at frequencies of several GHz. Despite this fact, the improvement with respect to the capacitive coupling technique, with reference to the RF signal transfer, is obtained by a circuit having an additional component, that is the inductor of the LC network.
It is also observed that the described techniques can be adopted for multi-stage differential amplifiers, but in this case, the number of reactive components doubles with a consequent increase of the chip area in which the circuit is integrated and therefore of the manufacturing cost.